function [ ] = mx_eyelink_last_message( )
%MX_EYELINK_LAST_MESSAGE Checks for and gets the last packet received, stores
% the data and the node address sent from.
%
% Returns:
% 0 if no message since last command sent, otherwise length of string.
% buf 	String buffer with return text message.
%
%----------------------------------------------------------------------------
% Copyright Eduardo Aponte 2013
% aponteeduardo@gmail.com